Oxygen-scavenging resin compositions having low haze

ABSTRACT

A resin composition provides good optical properties when stretched and efficient oxygen-scavenging, the resin composition comprising a film-forming polyester and an effective amount of oxygen-scavenging particles, wherein the particles have a particle size distribution such that particles of less than about 25 microns in size do not exceed a concentration defined by a formula that includes the apparent density of the particles. Another resin composition comprises a film-forming polyester and from about 50 to about 2500 parts by weight of iron per million by weight of the resin, wherein the amount of iron particles having a size of less than about 20 microns does not exceed about 800 parts per million by weight of the resin. A method is also provided for incorporating high levels of oxygen-scavenging particles into a film-forming polyester resin composition with low haze when stretched.

BACKGROUND OF THE INVENTION

Thermoplastic resins such as polyethylene terephthalate (PET) arecommonly used to manufacture packaging materials. PET processed underthe right conditions produces high strength articles with excellent gasbarrier properties. Foods, beverages, and medicines can deteriorate orspoil if exposed to oxygen. To improve shelf-life and flavor retentionof products such as foods, beverages, and medicines, therefore, thebarrier protection provided by PET is often supplemented with additionallayers of packaging material or with the addition of oxygen scavengers.

Adding a layer of gas barrier film is known as passive-barrierpackaging. Polyvinylidene dichloride (PVDC) is an example of a filmcommonly used for this purpose due to its excellent oxygen barrierproperties. This method is not preferred, however, because it adds costto packaging construction and does not reduce the levels of oxygenalready present in the package.

Adding oxygen scavengers to the PET resin is known as active-barrierpackaging. This approach to protecting oxygen-sensitive products istwo-fold; the packaging prevents oxygen from reaching the product fromthe outside, and also absorbs any oxygen present in the container. Insome applications, small packets or sachets containing oxygen scavengersare added to the packaging container. Iron powder is commonly used foroxygen scavenging in food packages. Iron reacts with the oxygen andforms iron oxide. Most applications also utilize a salt and a moistureabsorber as reaction-enhancing agents to increase the effectiveness ofthe iron powder. Even when a salt and a moisture absorber are added, onedifficulty with scavenger systems utilizing iron is the inefficiency ofthe oxidation reaction. High loadings of iron powder, on the order of1000-2500 parts per million, are typically required to obtain sufficientoxygen absorption. Unfortunately, previous attempts at preparing resincompositions comprising high levels of iron have resulted in packagingmaterials with poor optical properties. Typically, bottles prepared fromsuch resin compositions are dark in color or translucent. Haze valuesfor these bottles are generally high, and clarity is lacking.

Thus, there remains a need for packaging materials having acceptablevisual aspects and comprising oxygen scavenging resin compositions. Thisinvention relates to an oxygen-scavenging resin composition havingutility in packaging and other applications. More specifically, thisinvention relates to a film-forming, oxygen-scavenging polyester resincomposition having low haze. The present invention further relates to amethod for incorporating high levels of oxygen-scavenging particles intoa film-forming polyester resin composition with low haze.

BRIEF SUMMARY OF THE INVENTION

In general the present invention provides a resin compositioncomprising: a film-forming polyester; and an effective amount ofoxygen-scavenging particles comprising at least one oxygen-scavengingelement; wherein the particles have a particle size distribution suchthat particles of less than about 25 microns in size do not exceed aconcentration defined by the formula

ppm=512.3×d

wherein ppm is the approximate concentration of particles of less thanabout 25 microns in size in parts per million by weight, and d is theapparent density of the particles of less than about 25 microns in sizein grams per cubic centimeter.

The present invention also includes a resin composition comprising: afilm-forming polyester; and an effective amount of oxygen-scavengingiron particles, wherein the iron particles have a particle sizedistribution such that particles of less than about 25 microns in sizedo not exceed about 1250 parts per million by weight of the resin.

The present invention also includes a resin composition comprising afilm-forming polyester and from about 50 to about 2500 parts by weightof iron particles per million parts by weight of the resin, wherein theconcentration of iron particles of less than about 25 microns in sizedoes not exceed about 1250 parts per million by weight of the resin.

The present invention also includes a polyester resin composition foruse in forming transparent articles having low haze, the resincomposition comprising from about 50 to about 2500 parts by weight ofiron particles per million by weight of the resin, wherein saidtransparent articles have a Hunter haze value of about 10% or less.

The present invention also includes an article formed from a resincomposition comprising an effective amount of oxygen-scavengingparticles, wherein the Hunter haze value of the article is about 10% orless.

The present invention also includes a method for incorporating highlevels of oxygen-scavenging particles into a film-forming polyesterresin composition with low haze comprising the steps of: providing aneffective amount of oxygen-scavenging particles comprising at least oneoxygen-scavenging element, wherein the particles have a particle sizedistribution such that particles of less than about 25 microns in sizedo not exceed a concentration defined by the formula

ppm=512.3×d

wherein ppm is the approximate concentration of particles of less thanabout 25 microns in size in parts per million by weight, and d is theapparent density of the particles of less than about 25 microns in sizein grams per cubic centimeter; adding said oxygen-scavenging particlesto a polyester resin composition during one or more of the process stepsof: melt phase polymerization of the polyester; post polymerization andprior to pelletization; solid state polymerization of the polyester; andextrusion.

The present invention also includes a resin composition comprising: afilm-forming polyester; and particulates; wherein the particulates havea particle size distribution such that particles of less than about 25microns in size do not exceed a concentration defined by the formula

ppm=512.3×d

wherein ppm is the approximate concentration of particles of less thanabout 25 microns in size in parts per million by weight, and d is theapparent density of the particles of less than about 25 microns in sizein grams per cubic centimeter.

Advantageously, the present invention overcomes the problems associatedwith the prior art by providing a thermoplastic resin composition whichcontains an effective amount of iron or other oxygen scavenger and whichhas acceptable color and haze characteristics. The iron or other oxygenscavenger is present in an amount sufficient to effectively scavengeoxygen and provide longer shelf life for oxygen-sensitive materials. Theparticle size of the oxygen scavenger is optimized to provide effectivescavenging activity, while reducing dark coloration and haze.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a film-forming, oxygen-scavengingresin composition having low haze. Suitable thermoplastic polymers foruse in the present invention include any thermoplastic homopolymer orcopolymer. Examples of thermoplastic polymers include polyamides, suchas nylon 6, nylon 66 and nylon 612, linear polyesters, such aspolyethylene terephthalate, polybutylene terephthalate, polytrimethyleneterephthalate, and polyethylene naphthalate, branched polyesters,polystyrenes, polycarbonate, polyvinyl chloride, polyvinylidenedichloride, polyacrylamide, polyacrylonitrile, polyvinyl acetate,polyacrylic acid, polyvinyl methyl ether, ethylene vinyl acetatecopolymer, ethylene methyl acrylate copolymer, polyethylene,polypropylene, ethylenepropylene copolymers, poly(1-hexene),poly(4-methyl-1-pentene), poly(1-butene), poly(3-methyl-1-butene),poly(3-phenyl-1-propene) and poly(vinylcyclohexane). Preferably, thethermoplastic polymer used in the present invention comprises apolyester polymer or copolymer.

Polymers of the present invention can be prepared by conventionalpolymerization procedures well-known in the art. The polyester polymersand copolymers may be prepared by melt phase polymerization involvingthe reaction of a diol with a dicarboxylic acid, or its correspondingester. Various copolymers of multiple diols and diacids may also beused.

Suitable dicarboxylic acids include those comprising from about 6 toabout 40 carbon atoms. Specific dicarboxylic acids include, but are notlimited to, terephthalic acid, isophthalic acid, naphthalene2,6-dicarboxylic acid, cyclohexanedicarboxylic acid, cyclohexanediaceticacid, diphenyl-4,4′-dicarboxylic acid, 1,3-phenylenedioxydiacetic acid,1,2-phenylenedioxydiacetic acid, 1,4-phenylenedioxydiacetic acid,succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid,and the like. Specific esters include, but are not limited to, phthalicesters and naphthalic esters.

These acids or esters may be reacted with an aliphatic diol having fromabout 2 to about 10 carbon atoms, a cycloaliphatic diol having fromabout 7 to about 14 carbon atoms, an aromatic diol having from about 6to about 15 carbon atoms, or a glycol ether having from 4 to 10 carbonatoms. Suitable diols include, but are not limited to, 1,4-butenediol,trimethylene glycol, 1,6-hexanediol, 1,4-cyclohexanedimethanol,diethylene glycol, resorcinol, and hydroquinone.

Trifunctional or tetrafunctional comonomers can also be used. Suitablecomonomers include, but are not limited to, trimellitic anhydride,trimethylopropane, pyromellitic dianhydride, and pentaerythritol.Polyester-forming polyacids or polyols can also be used.

One preferred polyester is polyethylene terephthalate (PET) formed fromthe approximate 1:1 stoichiometric reaction of terephthalic acid, or itsester, with ethylene glycol. Another preferred polyester is polyethylenenaphthalate (PEN) formed from the approximate 1:1 stoichiometricreaction of naphthalene dicarboxylic acid, or its ester, with ethyleneglycol. Yet another preferred polyester is polybutylene terephthalate(PBT). Copolymers of PET, copolymers of PEN, and copolymers of PBT arealso preferred.

The esterification or polycondensation reaction of the carboxylic acidor ester with glycol typically takes place in the presence of acatalyst. Suitable catalysts include, but are not limited to, antimonyoxide, antimony triacetate, antimony ethylene glycolate,organomagnesium, tin oxide, titanium alkoxides, dibutyl tin dilaurate,and germanium oxide. These catalysts may be used in combination withzinc, manganese, or magnesium acetates or benzoates. Catalystscomprising antimony are preferred.

Another preferred polyester is polytrimethylene terephthalate (PTT). Itcan be prepared by, for example, reacting 1,3-propanediol with at leastone aromatic diacid or alkyl ester thereof. Preferred diacids and alkylesters include terephthalic acid (TPA) or dimethyl terephthalate (DMT).Accordingly, the PTT preferably comprises at least about 80 mole percentof either TPA or DMT. Other diols which may be copolymerized in such apolyester include, for example, ethylene glycol, diethylene glycol,1,4-cyclohexane dimethanol, and 1,4-butanediol. Aromatic and aliphaticacids which may be copolymerized include, for example, isophthalic acidand 2,6-naphthalene dicarboxylic acid.

Preferred catalysts for preparing PTT include titanium and zirconiumcompounds. Suitable catalytic titanium compounds include, but are notlimited to, titanium alkylates and their derivatives, titanium complexsalts, titanium complexes with hydroxycarboxylic acids, titaniumdioxide-silicon dioxide-co-precipitates, and hydratedalkaline-containing titanium dioxide. Specific examples includetetra-(2-ethylhexyl)-titanate, tetrastearyl titanate, diisopropoxy-bis(acetyl-acetonato)-titanium, di-n-butoxy-bis(triethanolaminato)-titanium, tributylmonoacetyltitanate, triisopropylmonoacetyltitanate, tetrabenzoic acid titanate, alkali titanium oxalatesand malonates, potassium hexafluorotitanate, and titanium complexes withtartaric acid, citric acid or lactic acid. Preferred catalytic titaniumcompounds are titanium tetrabutylate and titanium tetraisopropylate. Thecorresponding zirconium compounds may also be used.

The polymer of this invention may also contain small amounts ofphosphorous compounds, such as phosphates, and a catalyst such as acobalt compound, that tends to impart a blue hue.

The melt phase polymerization described above may be followed by acrystallization step, then a solid phase polymerization (SSP) step toachieve the intrinsic viscosity necessary for bottle manufacture. Thecrystallization and polymerization can be performed in a tumbler dryerreaction in a batch-type system. Alternatively, the crystallization andpolymerization can be accomplished in a continuous solid state processwhereby the polymer flows from one vessel to another after itspredetermined treatment in each vessel.

The crystallization conditions preferably include a temperature of fromabout 100° C. to about 150° C. The solid phase polymerization conditionspreferably include a temperature of from about 200° C. to about 232° C.,and more preferably from about 215° C. to about 232° C. The solid phasepolymerization may by carried out for a time sufficient to raise theintrinsic viscosity to the desired level, which will depend upon theapplication. For a typical bottle application, the preferred intrinsicviscosity is from about 0.65 to about 1.0 deciliter/gram. The timerequired to reach this viscosity may range from about 8 to about 21hours.

In one embodiment of the invention, the polyester used in the presentinvention may comprise recycled polyester.

The oxygen-scavenging resin composition of the present invention furthercomprises oxygen-scavenging particles. Suitable particles comprise atleast one oxidizable material capable of reacting with molecular oxygen.Desirably, materials are selected that do not react with oxygen soquickly that handling of the materials is impracticable. Therefore,stable oxygen-scavenging materials that do not readily explode or burnupon contact with molecular oxygen are preferred. From a standpoint offood safety, materials of low toxicity are preferred, however withproper precautions, this is not a limitation. The particles should notadversely affect the organoleptic properties of the final product.Preferably, the oxygen-scavenging particles comprise anoxygen-scavenging element selected from calcium, magnesium, scandium,titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper,zinc, silver, tin, aluminum, antimony, germanium, silicon, lead,cadmium, rhodium, and combinations thereof. More preferably, theoxygen-scavenging particles comprise an oxygen-scavenging elementselected from calcium, magnesium, titanium, vanadium, manganese, iron,cobalt, nickel, copper, zinc, or tin. Even more preferably, theoxygen-scavenging particles comprise iron. It will be understood thatthese oxygen-scavenging elements may be present as mixtures, incompounds such as oxides and salts, or otherwise combined with otherelements, with the proviso that the oxygen-scavenging elements arecapable of reacting with molecular oxygen. Metal alloys comprising atleast one oxygen-scavenging element are also suitable. Theoxygen-scavenging particles may contain impurities that do not affectthe practice of the present invention.

It is known in the art that certain substances enhance the oxygenscavenging reaction. In a preferred embodiment of the present invention,the oxygen-scavenging particles are pre-treated with one or morereaction-enhancing agents that facilitate the oxygen scavengingreaction. Any of the reaction-enhancing agents known in the art may beused.

In one embodiment of the present invention, the resin compositioncomprises metallic iron particles. Metallic iron is used so that theiron is able to react with oxygen in its function as an oxygenscavenger. Alloys or mixtures containing metallic iron may also be used.Furthermore, it is to be understood that the metallic iron may containimpurities that do not effect the practice of the present invention.

The present invention further relates to a method for incorporating highlevels of oxygen-scavenging particles into a polyester resin compositionwith low haze.

The oxygen-scavenging particles may be admixed with the thermoplasticpolymer during or after polymerization, with the polymer melt, or withthe molding powder or pellets from which the injection molded articlesare formed. Accordingly, the oxygen-scavenging particles may be addedduring any of the process steps, such as during melt phasepolymerization, after the melt phase polymerization (postpolymerization) but before pelletization, during solid statepolymerization, and during extrusion. Alternatively, a masterbatch ofoxygen-scavenging resin may be prepared, and then mixed or blended withadditional resin. Preferably, the masterbatch contains a relatively highamount of oxygen-scavenging particles, and the desired oxygen-scavengingparticle concentration in the product polymer is achieved by mixing orblending the masterbatch with an amount of additional resin.

In a preferred embodiment of the present invention, theoxygen-scavenging particles are pre-treated with a reaction-enhancingagent to facilitate the oxygen-scavenging reaction. Preferably, thispre-treatment occurs prior to admixing the oxygen-scavenging particleswith the thermoplastic polymer.

The oxygen-scavenging particles are present in an effective amount foradequate oxygen-scavenging ability. If too few oxygen-scavengingparticles are present, some oxygen may be able to pass through the resinwithout being scavenged. If too many oxygen-scavenging particles arepresent, the resin may be discolored prior to oxygen scavenging, or theresin may be rough in surface texture. The amount required for adequateoxygen-scavenging ability depends on such factors as the application,the type of polymer used, the amount of gas barrier protection desired,the type of oxygen-scavenging particles, the particle size of theoxygen-scavenging particles, and moisture content. Preferably, theoxygen-scavenging resin composition of the present invention comprisesat least about 50 parts per million oxygen-scavenging particles byweight of the resin. It has been found that film or bottle articlesformed from oxygen-scavenging resins comprising up to about 2500 partsper million oxygen-scavenging particles can have acceptable hazecharacteristics. For applications where haze is not an issue of concern,it will be appreciated that the amount of iron or otheroxygen-scavenging particles may be much higher. Further characterizationof the oxygen-scavenging particles that are necessary for practice ofthe present invention is provided hereinbelow.

It will be understood that, within any given sample of oxygen-scavengingparticles, the particles are not all the same size, but comprise a rangeof particle sizes. Thus, any given sample of oxygen-scavenging particleswill have a particle size distribution, which is a description of therange of particle sizes and the amounts of particles of each size. Sucha sample may also be described by an average particle size, as measuredby any of the standard techniques known in the art. The sample mayalternatively be described by a particle size range, or as less than orequal to a given particle size. These designations may be determined bysieving techniques, or other techniques known in the art.

The composition of the present invention may optionally further compriseone or more reaction-enhancing agents known in the art to facilitate theoxygen-scavenging reaction. Examples of known reaction-enhancing agentsinclude, but are not limited to, hydroscopic materials and salts. Thereaction-enhancing agents may be added to the polymer melt, or duringextrusion.

The composition of the present invention may optionally yet furthercomprise one or more components selected from the group consisting ofimpact modifiers, surface lubricants, denesting agents, stabilizers,crystallization aids, antioxidants, ultraviolet light absorbing agents,catalyst deactivators, colorants, nucleating agents, acetaldehydereducing agents, reheat reducing agents, fillers, branching agents,blowing agents, accelerants, and the like. These are generally wellknown and their presence or absence does not effect practice of thepresent invention which is based upon the addition of an effectiveamount of oxygen-scavenging particles to the composition.

The oxygen-scavenging resin of the present invention may be formed intobottle preforms and then into bottles. A “preform” is a formed structurethat is expanded in a mold to form a bottle. The manufacture of preformsand bottles is known in the art, and any one of a number of suitabletechniques can be used to prepare the preform and bottle. Alternately,the oxygen-scavenging resin may be formed into film, pouches, or otherpackaging material.

In general, polyester bottles are prepared in blow-molding processescarried out by heating the preform above the polyester glass transitiontemperature, placing the heated preform into a mold of the desiredbottle form, injecting air into the mold to force the preform into theshape of the mold, and ejecting the molded bottle from the mold onto aconveyor belt.

The oxygen-scavenging polyester resin of the present inventionadvantageously possesses both effective oxygen-scavenging functionalityand acceptable optical properties when stretched. The optical propertiesof polymers are related to both the degree of crystallinity and theactual polymer structure. Transparency is defined as the statepermitting perception of objects through a sample. Transmission is thelight transmitted. Transparency is measured as the amount of undeviatedlight. In other words, transparency is the original intensity of theincident radiation minus all light absorbed, scattered, or lost throughany other means.

Many polymers are transparent, but polymers that are transparent tovisible light may become opaque as the result of the presence ofadditives such as fillers, stabilizers, flame retardants, moisture, andgases. The opacity results from light-scattering processes occurringwithin the material. The light scattering reduces the contrast betweenlight, dark, and other colored parts of objects viewed through thematerial and produces a milkiness or haze in the transmitted image. Hazeis a measure of the amount of light deviating from the direction oftransmittancy of the light by at least 2.5 degrees.

The color and brightness of a polyester article can be observedvisually, and can also be quantitatively determined by a HunterLabColorQuest Spectrometer. This instrument uses the 1976 CIE a*, b*, andL* designations of color and brightness. Rd is also a measure ofbrightness. An a* coordinate defines a color axis wherein plus valuesare toward the red end of the color spectrum and minus values are towardthe green end. The b* coordinate defines a second color axis, whereinplus values are toward the yellow end of the spectrum and minus valuesare toward the blue end. Higher L* values indicate enhanced brightnessof the material.

While polyester crystallized through strain hardening (stretching) hasexcellent optical properties, including high transmittance and low lightscattering, particulate additives can reduce the transparency andincrease the haze. Generally, the haze of an article, such as a bottleor film, is measured visually. However, the haze of an article or resincan be quantitatively indicated by using ASTM method D1003, “Haze andLuminous Transmittance of Transparent Plastic.” The instrument used forthis method is a HunterLab ColorQuest Spectrometer. Two factors whichmust be taken into account when accurately measuring haze and comparinghaze values are the thickness of the article being measured, and theblow window.

In order to establish the proper temperature and processing time toobtain the lowest haze value due only to the crystallization process ofthe polyester resin, a blow window graph is constructed. The blow windowgraph shows haze as a function of the heat exposure time of the preform.The graph is usually constructed by creating isotherms and heating eachpreform at the same temperature for different lengths of time. Theheated preform is then stretched and the haze measurement is performedon the stretched portion. Several different temperatures are chosen.Generally, a resin will have a best temperature that produces the lowesthaze value, and that temperature is used to conduct the remainingevaluations. In the work described herein, one temperature was chosenand the parameter of time was varied.

Advantageously, it has been found that when the oxygen-scavengingparticles comprise iron, and the particle size distribution of the ironis such that particles of less than or equal to about 25 microns do notexceed about 1250 parts per million by weight of the resin, bottles andother packaging materials made by using the iron-containingthermoplastic resin composition have acceptable color and hazecharacteristics. Preferably, iron particles of less than about 20microns do not exceed about 800 parts per million by weight of theresin. More preferably, particles of less than about 20 microns do notexceed about 500 parts per million by weight of the resin. Even morepreferably, particles of less than about 20 microns do not exceed about100 parts per million by weight of the resin. Desirably, iron particlesof less than about 10 microns do not exceed about 800 parts per millionby weight of the resin. More desirably, iron particles of less thanabout 10 microns do not exceed about 500 parts per million by weight ofthe resin. Even more desirably, iron particles of less than about 10microns do not exceed about 100 parts per million by weight of theresin. Preferably, iron particles of less than or equal to about 5microns do not exceed about 500 parts per million by weight of theresin. More preferably, iron particles of less than or equal to about 5microns do not exceed about 100 parts per million by weight of theresin. Accordingly, it is to be understood that the recitationsthroughout the specification and claims of “less than about 25 microns”are intended to include the smaller iron particle sizes of 20 microns,10 microns, 5 microns, and less than 5 microns, depending upon the sizethat is preferred. Similarly, recitations of “do not exceed about 1250parts per million” are intended to include the smaller amounts of 800parts per million, 500 parts per million and 100 parts per million,depending upon the amount that is preferred. It will be appreciated thatparticles larger than the thickness of the bottles and other packagingmaterials made by using the high-iron thermoplastic resin compositionmay produce a rough surface, so that significant amounts of such largeparticles are to be avoided.

More generally, the advantageous particle size distribution of theoxygen-scavenging particles is determined as a function of the apparentdensity of the particles. The density of a metal powder particle is notnecessarily identical to the density of the material from which it isproduced because of the internal porosity of the particle. Apparentdensity refers to the weight of a unit volume of loose powder, usuallyexpressed in grams per cubic centimeter (g/cm³). The characteristics ofa powder that determine its apparent density are discussed in Peter K.Johnson, “Powder Metallurgy” in Kirk Othmer Encyclopedia of ChemicalTechnology, §§4.1, 4.2 (1995). Typical apparent density values for ironparticles reported by Johnson range from about 0.97 to about 3.4 gramsper cubic centimeter. The supplier of the iron particles employed hereinindicated that the apparent density of the particles was approximately2.44 grams per cubic centimeter. It will be understood that preferredconcentrations and particle size distributions of iron particles recitedherein apply to iron particles having an apparent density of from about2.3 to about 2.5 grams per cubic centimeter. When particles comprisingiron or other materials and having an apparent density significantlydistinct from this range are employed, the advantageous particles sizedistribution of the particles is determined by the following formulae.

Preferably, the particle size distribution of the oxygen-scavengingparticles is such that particles of less than or equal to about 25microns do not exceed a concentration defined by the formula

wherein ppm is the approximate concentration of particles of less thanabout 25 microns in size in parts per million by weight, and d is theapparent density of the particles of less than about 25 microns in sizein grams per cubic centimeter. The constant 512.3 in the precedingformula was derived from a calculation based upon a particle sizedistribution such that particles of less than or equal to about 25microns do not exceed a concentration of 1250 parts per million byweight, and wherein the particles have an apparent density of about 2.44grams per cubic centimeter.

More preferably, the particle size distribution of the oxygen-scavengingparticles is such that particles of less than or equal to about 20microns do not exceed a concentration defined by the formula

ppm=327.9×d

wherein ppm is the approximate concentration of particles of less thanabout 20 microns in size in parts per million by weight, and d is theapparent density of the particles of less than about 20 microns in sizein grams per cubic centimeter. The constant 327.9 was determined in thesame manner as in the preceding formula, as were each of the formulaewhich follow.

Even more preferably, the particle size distribution of theoxygen-scavenging particles is such that particles of less than or equalto about 20 microns do not exceed a concentration defined by the formula

ppm=204.9×d

wherein ppm is the approximate concentration of particles of less thanabout 20 microns in size in parts per million by weight, and d is theapparent density of the particles of less than about 20 microns in sizein grams per cubic centimeter.

Still more preferably, the particle size distribution of theoxygen-scavenging particles is such that particles of less than or equalto about 20 microns do not exceed a concentration defined by the formula

ppm=41.0×d

wherein ppm is the approximate concentration of particles of less thanabout 20 microns in size in parts per million by weight, and d is theapparent density of the particles of less than about 20 microns in sizein grams per cubic centimeter.

Desirably, the particle size distribution of the oxygen-scavengingparticles is such that particles of less than or equal to about 10microns do not exceed a concentration defined by the formula

ppm=327.9×d

wherein ppm is the approximate concentration of particles of less thanabout 10 microns in size in parts per million by weight, and d is theapparent density of the particles of less than about 10 microns in sizein grams per cubic centimeter.

More desirably, the particle size distribution of the oxygen-scavengingparticles is such that particles of less than or equal to about 10microns do not exceed a concentration defined by the formula

ppm=204.9×d

wherein ppm is the approximate concentration of particles of less thanabout 10 microns in size in parts per million by weight, and d is theapparent density of the particles of less than about 10 microns in sizein grams per cubic centimeter.

Even more desirably, the particle size distribution of theoxygen-scavenging particles is such that particles of less than or equalto about 10 microns do not exceed a concentration defined by the formula

ppm=41.0×d

wherein ppm is the approximate concentration of particles of less thanabout 10 microns in size in parts per million by weight, and d is theapparent density of the particles of less than about 10 microns in sizein grams per cubic centimeter.

Preferably, the particle size distribution of the oxygen-scavengingparticles is such that particles of less than or equal to about 5microns do not exceed a concentration defined by the formula

ppm=204.9×d

wherein ppm is the approximate concentration of particles of less thanabout 5 microns in size in parts per million by weight, and d is theapparent density of the particles of less than about 5 microns in sizein grams per cubic centimeter.

More preferably, the particle size distribution of the oxygen-scavengingparticles is such that particles of less than or equal to about 5microns do not exceed a concentration defined by the formula

ppm=41.0×d

wherein ppm is the approximate concentration of particles of less thanabout 5 microns in size in parts per million by weight, and d is theapparent density of the particles of less than about 5 microns in sizein grams per cubic centimeter.

The oxygen-scavenging resin having low haze, according to the presentinvention, can be stretched into bottles having a Hunter haze number of,preferably, less than about 10 percent, more preferably less than about8 percent, and even more preferably less than about 5 percent, atoptimum blow window conditions. While higher than the haze numbers forpolyester samples comprising no iron or other oxygen-scavengingparticles, these haze values are well within the range of valuesacceptable for many commercial applications. Furthermore, someapplications may tolerate a higher haze value, depending upon thethickness of the film and the tint of the film. When a film or bottlewall or other article has a thickness of from about 12 to about 15 mils,and is not significantly tinted, the haze values stated above giveacceptable optical characteristics. When a film is stretched thinnerthan this, higher haze values will still give acceptable opticalcharacteristics. Likewise, when a tint is added, higher haze values areacceptable. Accordingly, if a higher haze can be tolerated, then higherlevels of oxygen-scavenging particles, for a given particle size, can bepresent and still produce acceptable optical characteristics.

The present invention also provides a resin composition comprising: afilm-forming polyester; and particulates; wherein the particulates havea particle size distribution such that particles of less than about 25microns in size do not exceed a concentration defined by the formula

ppm=512.3×d

wherein ppm is the approximate concentration of particles of less thanabout 25 microns in size in parts per million by weight, and d is theapparent density of the particles of less than about 25 microns in sizein grams per cubic centimeter. The particulates may or may not compriseoxygen-scavenging elements. Suitable particulates include, but are notlimited to, ceramic, plastic, and metal particulates, molecular sieves,and the like.

In order to demonstrate the practice of the present invention, thefollowing examples have been prepared and tested as described in theGeneral Experimentation Section disclosed hereinbelow. The examplesshould not, however, be viewed as limiting the scope of the invention.The claims will serve to define the invention.

General Experimentation

A PET resin was prepared by reacting terephthalic acid and ethyleneglycol to make a melt phase polymer, sometimes referred to as a feedpolymer. Other polyester resins containing isophthalate or naphthalatewere also prepared. This low molecular weight feed polymer wascrystallized and solid state polymerized to prepare a high molecularweight PET base resin. Samples of iron particles having variousparticles sizes were obtained. The apparent density of the ironparticles was approximately 2.44 grams per cubic centimeter. Thus, theiron particles used in Example No. 3 had a particle size range of about25 to about 38 microns. It will be understood that such a sample can beprepared, for example, by using sieves. The iron particles were added topolyester resin, by using a metered feeder on a twin-screw extruder, toform a masterbatch of resin containing 2 percent by weightiron-containing resin composition. This masterbatch was blended with thebase resin to obtain the desired concentration. The base resin/ironmixtures were dried under vacuum at 325° F. (163° C.) for 18 hours. Thedried resins were transferred to a Novotec drying hopper of a Nissei ASB50T Injection Blow-Molding machine. The hopper was heated to 325° F.(163° C.) and set for a dew point of −40° F. (−40° C.).

The bottle preforms were heated and blown into bottles in a two-stepprocess. First, the preforms were prepared on a Mini-jector or Nisseimachine. Then, the bottles were blown from their preforms on aCincinnati Milacron Reheat Blow Lab (RHB-L) blow molding machine. Thepreforms were prepared on the Mini-jector using a cycle time of 45second, inject time of 15 seconds, with a rear heater temperature of270° C., a front heater temperature of 275° C., and a nozzle heat of275° C. The inject pressure was between about 1000 and about 1500 psig.The oven temperature on the Milacron RHB-L was from about 163 to about177° C. The exposure time was from about 31 to about 52 seconds. Thehaze measurements were taken on the bottle side-wall, which is thethinned, stretched portion.

The iron particle concentration, average iron particle size, and thehaze values at a constant sample thickness and optimum blow windowconditions are summarized in Tables 1 and 2. Comparative Example Nos. 1,6, and 11 contained no iron particles.

TABLE 1 Iron Particles in Stretched Polyester Film Compositions OptimumFe conc. Particle size reheat time Example No. (ppm) (microns) (sec)Haze (%) 1 0 — 43 1.5 2 1250 ≦25 49 7.56 3 1250 25-38 49 4.53 4 125038-45 52 4.58 5 1250 45-75 52 4.41 6 0 — 43 1.5 7 2500 ≦25 46 14.08 82500 25-38 46 9.13 9 2500 38-45 46 8.45 10 2500 45-75 40 8.56

TABLE 2 Iron Particles in Stretched Polyester Film Compositions and HazeValues Optimum Particle reheat Example Fe conc. size time Haze No. (ppm)(microns) (sec) (%) Rd L* 11 0 — 43 1.5 78.13 90.89 12 100 1-3 46 5.175.83 89.78 13 250 1-3 40 6.98 73.44 88.66 14 500 1-3 46 9.12 68.3386.17 15 800 1-3 46 11.63 64.05 83.99 16 1000 1-3 46 16.44 53.39 78.1 17100 3-5 49 4.55 75.78 89.76 18 250 3-5 49 6.74 75.71 79.73 19 500 3-5 469.04 72.64 88.27 20 800 3-5 46 11.8 70.45 87.21 21 1000 3-5 46 12.9963.46 83.68 22 100 7-9 49 5.4 77.4 90.51 23 250 7-9 46 6.85 75.94 89.8324 500 7-9 43 8.49 73.72 88.79 25 800 7-9 49 7.83 72.18 88.06 26 10007-9 46 8.81 70.56 87.27

Haze values of less than 10% are obtained, even at iron levels of 2500ppm, when the iron particle size is greater than about 25 microns, asshown in Table 1. At 1250 ppm iron, and also at 2500 ppm iron, thehighest haze values were obtained when the average particle size wasless than or equal to about 25 microns, i.e., Example Nos. 2 and 7,respectively. Nevertheless, when the iron particle size is less than orequal to about 25 microns, haze values of less than 10% are obtained atiron levels up to about 1250 ppm. As shown in Table 2, when the ironparticle size is less than or equal to about 9 microns, haze values ofless than 10% are obtained at iron levels up to about 800 ppm.Furthermore, when the iron particle size is less than or equal to about5 microns, haze values of less than 10% are obtained at iron levels upto about 500 ppm.

As should now be understood, the present invention overcomes theproblems associated with the prior art by providing a thermoplasticresin composition which contains an effective amount ofoxygen-scavenging particles and which has acceptable color and hazecharacteristics. The resulting resin can be used to form transparentbottles, films, and other packaging materials. These materials compriseoxygen-scavenging particles in an amount sufficient to effectivelyscavenge oxygen and provide longer shelf life for oxygen-sensitivematerials. Furthermore, these materials have acceptable color and hazecharacteristics.

While the best mode and preferred embodiment of the invention have beenset forth in accord with the Patent Statutes, the scope of thisinvention is not limited thereto, but rather is defined by the attachedclaims. Thus, the scope of the invention includes all modifications andvariations that may fall within the scope of the claims.

What is claimed is:
 1. A resin composition comprising: a film-formingpolyester; and an effective amount of oxygen-scavenging particlescomprising at least one oxygen-scavenging element capable of reactingwith molecular oxygen; wherein the particles have a particle sizedistribution such that particles of greater than and less than about 25microns in size are present, but those particles less than about 25microns in size do not exceed a concentration defined by the formulappm=512.3×d wherein ppm is the approximate concentration of particles ofless than about 25 microns in size in parts per million by weight, and dis the apparent density of the particles of less than about 25 micronsin size in grams per cubic centimeter.
 2. The resin composition of claim1, wherein said polyester comprises linear polyesters or branchedpolyesters.
 3. The resin composition of claim 1, wherein said polyestercomprises polyethylene terephthalate, copolymers of polyethyleneterephthalate, polyethylene naphthalate, copolymers of polyethylenenaphthalate, polybutylene terephthalate, copolymers of polybutyleneterephthalate, polytrimethylene terephthalate, or copolymers ofpolytrimethylene terephthalate.
 4. The resin composition of claim 1,wherein said oxygen-scavenging element comprises calcium, magnesium,scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel,copper, silver, zinc, tin, aluminum, antimony, germanium, silicon, lead,cadmium, rhodium, or combinations thereof.
 5. The resin composition ofclaim 1, wherein said oxygen-scavenging element comprises iron.
 6. Theresin composition of claim 1, wherein said effective amount ofoxygen-scavenging particles is from about 50 to about 2500 parts permillion by weight of the resin.
 7. The resin composition of claim 1,wherein said oxygen-scavenging particles have a particle size range ofabout 20 to about 70 microns.
 8. The resin composition of claim 1,wherein said particles of less than about 25 microns in size have anapparent density of about 2.44 grams per cubic centimeter.
 9. The resincomposition of claim 1, wherein particles of less than about 20 micronsin size have an apparent density of about 2.44 grams per cubiccentimeter, and do not exceed a concentration of about 800 parts permillion by weight of the resin.
 10. The resin composition of claim 1,wherein said oxygen-scavenging particles are pre-treated with one ormore reaction-enhancing agents.
 11. The resin composition of claim 1,wherein bottles produced from said resin have a Hunter haze value ofabout 10% or less.
 12. A resin composition comprising: a film-formingpolyester; and an effective amount of oxygen-scavenging iron particles,wherein the iron particles have a particle size distribution such thatparticles of less than about 25 microns in size are present, but do notexceed about 1250 parts per million by weight of the resin.
 13. Theresin composition of claim 12, wherein said polyester comprises linearpolyesters or branched polyesters.
 14. The resin composition of claim12, wherein said polyester comprises polyethylene terephthalate,copolymers of polyethylene terephthalate, polyethylene naphthalate,copolymers of polyethylene naphthalate, polybutylene terephthalate,copolymers of polybutylene terephthalate, polytrimethyleneterephthalate, or copolymers of polytrimethylene terephthalate.
 15. Theresin composition of claim 12, wherein said effective amount of ironparticles is from about 50 to about 2500 parts per million by weight ofthe resin.
 16. The resin composition of claim 12, wherein said ironparticles have a particle size range of about 20 to about 70 microns.17. The resin composition of claim 12, wherein particles of less thanabout 20 microns in size do not exceed about 800 parts per million byweight of the resin.
 18. The resin composition of claim 12, wherein saidoxygen-scavenging particles are pre-treated with one or morereaction-enhancing agents.
 19. The resin composition of claim 12,wherein bottles produced from said resin have a Hunter haze value ofabout 10% or less.
 20. A resin composition comprising a film-formingpolyester and from about 50 to about 2500 parts by weight ofoxygen-scavenging iron particles per million parts by weight of theresin, wherein the concentration of iron particles of less than about 25microns in size does not exceed about 1250 parts per million by weightof the resin.
 21. The resin composition of claim 20, wherein saidpolyester comprises linear polyesters or branched polyesters.
 22. Theresin composition of claim 20, wherein said polyester comprisespolyethylene terephthalate, copolymers of polyethylene terephthalate,polyethylene naphthalate, copolymers of polyethylene naphthalate,polybutylene terephthalate, copolymers of polybutylene terephthalate,polytrimethylene terephthalate, or copolymers of polytrimethyleneterephthalate.
 23. The resin composition of claim 20, wherein said ironparticles have a particle size range of from about 20 to about 70microns.
 24. The resin composition of claim 20, wherein particles ofless than about 20 microns in size do not exceed about 500 parts permillion by weight of the resin.
 25. The resin composition of claim 20,wherein said oxygen-scavenging particles are pre-treated with one ormore reaction-enhancing agents.
 26. The resin composition of claim 20,wherein bottles produced from said resin have a Hunter haze value ofabout 10% or less.
 27. A polyester resin composition for use in formingtransparent articles having low haze, the resin composition comprisingfrom about 50 to about 2500 parts by weight of iron particles permillion by weight of the resin, wherein said transparent articles have aHunter haze value of about 10% or less.
 28. The resin composition ofclaim 27, wherein said polyester comprises polyethylene terephthalate,copolymers of polyethylene terephthalate, polyethylene naphthalate,copolymers of polyethylene naphthalate, polybutylene terephthalate,copolymers of polybutylene terephthalate, polytrimethyleneterephthalate, or copolymers of polytrimethylene terephthalate.
 29. Theresin composition of claim 27, wherein said iron particles have aparticle size distribution such that particles of less than about 25microns in size do not exceed a concentration defined by the formulappm=512.3×d wherein ppm is the approximate concentration of particles ofless than about 25 microns in size in parts per million by weight, and dis the apparent density of the particles of less than about 25 micronsin size in grams per cubic centimeter.
 30. A method for incorporatinghigh levels of oxygen-scavenging particles into a film-forming polyesterresin composition with low haze comprising the steps of: providing aneffective amount of oxygen-scavenging particles comprising at least oneoxygen-scavenging element capable of reacting with molecular oxygen,wherein the particles have a particle size distribution such thatparticles of greater than and less than about 25 microns in size arepresent, but those particles less than about 25 microns in size do notexceed a concentration defined by the formula ppm=512.3×d wherein ppm isthe approximate concentration of particles of less than about 25 micronsin size in parts per million by weight, and d is the apparent density ofthe particles of less than about 25 microns in size in grams per cubiccentimeter; adding said oxygen-scavenging particles to a polyester resincomposition during one or more of the process steps of melt phasepolymerization of the polyester; post polymerization and prior topelletization; solid state polymerization of the polyester; andextrusion.
 31. The method of claim 30, wherein said step of addingoxygen-scavenging particles to a polyester resin composition produces amasterbatch of oxygen-scavenging resin; and wherein said method furthercomprises the step of adding said masterbatch to additional resin. 32.The method of claim 30, wherein said polyester resin comprisespolyethylene terephthalate, copolymers of polyethylene terephthalate,polyethylene naphthalate, copolymers of polyethylene naphthalate,polybutylene terephthalate, copolymers of polybutylene terephthalate,polytrimethylene terephthalate, or copolymers of polytrimethyleneterephthalate.
 33. The method of claim 30, wherein saidoxygen-scavenging particles comprise oxidizable forms of calcium,magnesium, scandium, titanium, vanadium, chromium, manganese, iron,cobalt, nickel, copper, silver, zinc, tin, aluminum, antimony,germanium, silicon, lead, cadmium, rhodium, or combinations thereof. 34.The method of claim 30, wherein said oxygen-scavenging element comprisesiron.
 35. The method of claim 30, wherein said effective amount ofoxygen-scavenging particles is from about 50 to about 2500 parts permillion by weight of the resin.
 36. The method of claim 30, wherein saidparticles of less than about 25 microns in size have an apparent densityof about 2.44 grams per cubic centimeter.
 37. The method of claim 30,wherein particles of less than about 20 microns in size have an apparentdensity of about 2.44 grams per cubic centimeter, and do not exceed aconcentration of about 800 parts per million by weight of the resin. 38.The method of claim 30, wherein said oxygen-scavenging particles arepre-treated with one or more reaction-enhancing agents.
 39. The methodof claim 30, wherein bottles produced from said resin have a Hunter hazevalue of about 10% or less.
 40. A resin composition comprising: afilm-forming polyester; and particulates comprising oxygen-scavengingparticles capable of reacting with molecular oxygen; wherein theparticulates have a particle size distribution such that particles ofgreater than and less than about 25 microns in size are present, butthose particles less than about 25 microns in size do not exceed aconcentration defined by the formula ppm=512.3×d wherein ppm is theapproximate concentration of particles of less than about 25 microns insize in parts per million by weight, and d is the apparent density ofthe particles of less than about 25 microns in size in grams per cubiccentimeter.